i fish a lot (posted some pics recently)
i always release them as i go fishing for carp and they live for years, is great when your a regular to a well maintained lake where people care about the fish, you get to know the fish in there and is really good feeling to catch one, put it back and see again a year later.
It can be a cruel hooby tho, when u go to a lake and see people fishing every 5m all the way around the lake, puts pressure on the fish, also a lot of people don't really care for the fish, or appreciate the fact that they are incredible things, not just a fishy lump that u drag onto bank and sling back.
i even treat the fish i catch with carp care products